Anti-cavitation valve

ABSTRACT

A valve in the circuit between a hydraulic control valve and a double acting hydraulic or fluid motor to prevent cavitation in the expanding working space of the motor by controlling the exhaust flow from the contracting working space. The anticavitation valve is responsive to the pressure maintained in the expanding working space by being connected through a logic circuit to the pressure in the expanding working space such that the response of the anti-cavitation valve will be varied in accorance with the pressure level at which the hydraulic motor is operating. In addition, the anti-cavitation valve functions to lock the hydraulic motor when the manual control valve is in its neutral position or when the supply pump is inoperative due to the prime mover for the pump being shut-off and the manual valve is actuated.

ited States Glore ,1 ntent 11 1 Oct. 28, 1975 ANTl-CAVITATION VALVE Prima Examiner-Irwin C. Cohen 75 Inventor: Noel M. Glore W te Ohi ry OS I O Attorney, Agent, or Firm-Robert L. Zieg [73] Assignee: Borg-Warner Corporation, Chicago,

Ill.

22 Filed: Dec. 7, 1973 [57] ABSTRACT [21] Appl N0: 422,636 A valve in the circuit between a hydraulic control valve and a double actmg hydraulic or fluid motor to prevent cavitation in the expanding working space of [52] U5. CI. 91/420 th ot b ont olling the exhaust flow from the l Cl? F153 F153 13/042 contracting working space. The anti-cavitation valve is Fleld 0f Search 25l/21O responsive to the pressure maintained in the expanding working space by being connected through a logic References Cited circuit to the pressure in the expanding working space UNITED STATES PATENTS such that the response of the anti-cavitation valve will 427,152 5/1890 Buttz 251/210 x be in 399919999 9 the Pressure at 3,125,324 3/1964 Vivier 1. 91/420 X whlch the hydraullc motor OPeratmg- In addltlon, 3,169,453 2/1965 Westveer 91/420 he n avi tion v lve functions to lock the hydrau- 3,l81,431 5/1965 Hein et a1. 91/420 X lic motor when the manual control valve is in its neu- 3,213,374 10/1965 Schmiel et a1. 91/42 X tral position or when the supply pump is inoperative McMillen t due to the prime mover for the pump being Shut off 3,802,660 4 1974 Fletcher et a1 251/210 x and the manual valve is actuated FOREIGN PATENTS OR APPLICATIONS 1,119,615 12/1961 Germany 91 420 7 2 Drawmg F'gures 16 IO 46 140 no 152 155 50 H8 1 124 1 A 162 8 92" 116 1 2 I n 42 1 1 a 130 154 164 1 I ,32 r46 1 J s2 36! 11 44/ i if q i 1K 12 82 66 US. Patent Oct. 28, 1975 3,915,067

ANTI-CAVITATION VALVE SUMMARY OF INVENTION Hydraulic circuits are known in the art in which valves are provided to control cavitation in a hydraulic motor, particularly a hydraulic motor of the double acting type moving a load which in a phase of operation due to its weight tends to assist motor movement. Difficulty is found in controlling the motor to prevent cavitation while at the same time maintaining proper function of the anti-cavitation valve with various pressure levels in the hydraulic motor. In addition, separate valves are normally provided to provide a load check operation when the manual valve is returned to neutral to prevent a load, which has been lifted or tilted by the hydraulic motor, from moving under its own weight when no pressure is being supplied. The present valve provides both the load check function and the anticavitation function since it is connected through a logic circuit which is adapted to always connect to the chamber of the hydraulic motor being supplied with fluid pressure. The anti-cavitation valve can thus be connected in the fluid connection between the hydraulic motor and the manual valve which is the side of the circuit, for example, which will have pressure created in it by the load moving the hydraulic motor when the manual valve is in its neutral position. The anticavitation therefore can conveniently serve as a load check valve with hydraulic motors used for lifting loads and/or tilting loads, but due to its having a fluid responsive area always connected to the pressure being supplied to the fluid motor, can provide the anticavitation function while being of relatively simple construction as compared to prior art valves. In addition, the anti-cavitation valve permits free flow of hydraulic fluid when the hydraulic motor is being actuated in a direction in opposition to the load where the above described cavitation problem does not exist.

DESCRIPTION OF THE DRAWINGS Referring to the drawings;

FIG. 1 shows a hydraulic circuit utilizing the valve of the present invention in schematic form; and

FIG. 2 shows a cross-sectional view taken along lines 22 of a portion of the anti-cavitation valve of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the anti-cavitation valve of the present invention is illustrated in its normal environment in a hydraulic control circuit. Included in the circuit disclosed in FIG. 1 is a manual control valve 12 for controlling operation of a fluid or hydraulic motor 14 of the double acting type, which as illustrated, is connected to a tilt mechanism 16 for a load as, for example, on a lift truck. The circuit further includes a fluid or hydraulic pump 18 of the constant displacement type and an unloading or bypass valve 20. A fluid sump 22 is provided for the control circuit. Operating in conjunction with the manual control valve 12 and the fluid motor 14 is a logic system or selective means 24.

The manual control valve 12 is of the type as described in US. Pat. Nos. 3,592,216 and 3,526,247 of common assignee. For a detailed description of the manual control valve 12, reference may be had to the mentioned prior patents. The control valve 12 generally includes work or motor ports 30 and 32, control ports 34, 36, inlet means or port 38 and an exhaust port 40. The manual control valve 12 has a neutral position 42 schematically illustrated and actuating positions 44 and 46 schematically illustrated.

The fluid motor 14 includes a piston 48 connected to operate the tilt mechanism 16, for example, the frame on a lift truck. The fluid motor 14 includes a fluid chamber 50 and a fluid chamber 52 on opposite sides of the piston 48.

The logic system 24 comprises a primary logic system including a shuttle valve 56 and secondary logic system including a shuttle valve 58. Primary shuttle valve 56 is a three port valve connected by conduits 60 and 62 to control ports 34 and 36, respectively, of manual control valve 12. The shuttle valve 56 has a ball 64 therein and an outlet conduit 66. It will be seen that the valve 56 will select the highest pressure existing in control ports 34, 36 and connect the pressure to outlet conduit 66 when the manual valve is in one of its working or op erating positions 44 or 46. Connected to conduit 66 is the secondary shuttle valve 58. Shuttle valve 58 is connected to an outlet conduit 70' which is in turn connected to the unloading valve 20. The secondary shuttle valve 58 is also connected to the conduit 72 which may be connected to and in series with secondary shuttle valves 58 of other manual control valve work stations in a system having multiple: manual control valves. A system of this type is illustrated and described in US. Pat. No. 3,693,506 of common assignee.

A fluid conduit or line connects work port 30 of manual control valve 12 to chamber 52 of fluid motor 14 and a fluid conduit or line 82 connects work port 32 of manual valve 12 to chamber 50 of fluid motor 14. A conduit 84 connects exhaust port 40 to the sump 22. A conduit 86 is connected to anti-cavitation 10 and to the sump 22. A conduit 88 connects pump 18 to inlet port 38 and is thus the fluid supply conduit for the system. A conduit 90 connects the outlet of pump 18 to the unloading valve 20. A conduit 92 connects conduit 66 of the primary logic valve 56 to the anti-cavitation valve 10. Conduit 98 connects the unloading valve to the sump 22. Conduit 70 is connected to exhaust conduit 84 by a relief valve 100.

The operation of the control system, as thus far de' scribed, is completely explained in prior mentioned US. Pat. Nos. 3,693,506 and 3,526,247. In general, the control system operates to actuate and control a fluid motor such as fluid motor 14 illustrated. The manual valve 12 has a operating position as, for example, 44 which connects pressure in inlet conduit 38 to conduit 80 to act on piston 48 to move piston 48 to the right. When the valve is in this position, a variable orifice is provided in the valve as described in the prior mentioned US. Pat. No. 3,526,247 by means of which the response of the fluid motor can be varied in accordance with the size of the orifice set by the operator. As described in the mentioned patent, the unloading valve 20 operates to maintain a constant pressure drop across the variable orifice provided in the manual valve 12 providing a responsiveness of valve 12 which is desired by an operator so that as the orifice size is varied the flow will change to provide a proportional effect on fluid motor 14.

The unloading valve 20 as described in the aforementioned patents is connected to conduit 70 and its response depends on the pressure in conduit 70. Conduit 70 is connected by the logic system 24, even in the case of a plurality of work stations and manual valves 12, to the highest work port pressure existing of any of the valves such as manual control valve 12. The construction of the manual control valve is such that each of the control ports 34 or 36 will be connected to its corresponding work port 30 or 32 and the load pressure therein due to the construction of the valve 12 as schematically illustrated in FIG. 1. This highest work port pressure is connected by the primary logic valve 56 to conduit 66 and thus through secondary logic valve 58 to the unloading valve 20. The unloading valve is connected to the outlet of pump 18 through conduit 90 and will control the effective output of the pump 18 in response to the fluid pressure received from conduit 70 thus providing a load responsive system for actuating the fluid motor 14. As mentioned above, a detailed description of this system and the construction of the manual valve 12 can be found in the aforementioned patents and the invention herein described relates to the anti-cavitation built into the system described.

Anti-cavitation valve 10 is particularly adapted to operate with a system having'a fluid motor of the double acting type wherein a logic system is provided so that a single connection can be made to the highest work cylinder pressure available. Anti-cavitation valve 10 is illustrated as mounted in a valve body 110 and has a piston 112. Piston 112 is of two diameters having a large land 114 and a relatively smaller land 116. Piston 112 has a nose portion 118 having a conical head portion 120 thereon. Piston nose portion 118 has a surface area 119 thereon which is exposed to pressure in conduit 80. Piston 112 is hollow having a central bore 122. The central bore 122 is connected by ports 124 to the exterior of the piston in the area adjacent nose portion 120. Due to the difference in diameters between land 114 and 116, a shoulder 126 is provided which provides a fluid responsive or differential area which is subjected to pressure in conduit 92 for actuating piston 112.

Piston 112 is illustrated with O-ring seals 130 and 132 on lands 114 and 116, respectively, to provide a fluid seal within the valve body 110. Also provided within the valve body 110 and as particularly illustrated in FIG. 2 is a seat member 140. Seat member 140 has a small bore 142 and a counter-bore portion 144 of larger diameter together defining a passage therethrough. A conical seat 146 is provided extending between the bore 142 and counter-bore 144 which serves as a seat for the head portion 120 of piston 112 when it is in engagement with seat member 140. Also provided is a metering slot or damping means 148 at the end of the seat member 140 in the area of counter-bore 144. As will be apparent, with systems of higher flow requirement, more than one metering slot 148 may be provided in seat member 140.

Internal of the large land portion 114 of piston 112 is a bore 150 which receives a sleeve member 152. An O-ring 154 provides a fluid seal between piston 112 and sleeve member 152. The sleeve member 152 thus serves to maintain a fluid seal as the piston 112 moves with respect to sleeve member 152. An end plug 156 is threadingly engaged within the valve body 110 at the right end of valve 10 as illustrated in FIG. 1. The end plug 156 has an internal bore 158 which receives sleeve member 152. An O-ring 160 is provided in the internal bore 158 in engagement with sleeve member 152. End plug 156 has a central bore 162 therethrough. A spring 164 is provided mounted around sleeve member 152 and in engagement with piston 112 and end plug 156. Spring 164 thus serves to act as a return spring to urge piston 112 to the left to engage head portion in seat 146 of the seat member as will be described.

Alternatively, the piston 112 and sleeve member 152 can be made integral or one-piece with the section 152 then being slideable in end plug 156. This would eliminate the need for O-ring 154.

The anti-cavitation valve 10 is operative to prevent cavitation in the chamber 50 of fluid motor 14 when the piston 48 is moving to tilt the arms 16 of the lift truck. As will be apparent as the tilt function is being carried out by supplying fluid pressure to chamber 50, the load on the lift truck frame will tend to pull piston 48 at a speed greater than that being normally produced by pressure in chamber 50 thus providing a tendency to induce fluid cavitation within chamber 50. Anti-cavitation valve 10 serves to restrict the flow of fluid as fluid pressure is created by the contracting of chamber 52 while fluid pressure is provided to expand chamber 50 when the load is being tilted, for example.

As will be seen, when piston 112 has its head portion 120 in engagement with seat 146 fluid pressure cannot escape from fluid chamber 52 and thus the fluid motor would be locked. The speed at which the piston 48 can contract chamber 52 can thus be varied by the amount of restriction induced by the piston 112 due to the size of the orifice which will be created between the head portion 120 and seat 146 when the piston 112 is not in engagement with the seat 146. As stated above, spring 164 tends to move piston 112 to its engaged position completely blocking flow from chamber 52. However, shoulder 126 is connected by conduit 92 to the highest work port pressure in work ports 30 or 32 by the manual valve 12 through the medium of control ports 34 and 36.

In the case of pressure being supplied to chamber 50 of fluid motor 14 namely, position 46 of manual 12, the pressure in conduit 82 to supply chamber 50 will also be connected through control port 36 to conduit 66 and conduit 92 to act on shoulder or fluid responsive area 126. Thus the piston 112 has a bias to the right against the force of spring 164 depending upon the working pressure in chamber 50 of fluid motor 14.

Thus as described, the anti-cavitation valve 10 will control the rate of exhaust flow from chamber 52 to prevent cavitation in chamber 50. The response of the anti-cavitation valve 10 is varied by the actual pressure being supplied to chamber 50 as described above and thus the system can be tailored to prevent cavitation under a wide range of working pressures. Metering slot 148 is effective to prevent oscillation and abrupt closure or engagement of head portion 120 with seat 146 since when the comer 121 of head portion 120, as piston 112 moves to the left is located in the area of metering slot 148, pressure is communicated to the exterior conical surface of head portion 120 creating a force working against the movement of the piston 1 12 to the left to dampen the movement of piston 112 and thus provide for smooth operation.

The anti-cavitation valve provides the further function of acting as a load check valve. When control valve 12 is in its neutral position 42, piston 112 will be moved into engagement with seat 146 since in the neutral position there is no pressure communicated through conduit 92 to act on shoulder 126 and oppose the force of spring 164. Thus if the system is in neutral with a load on the frame, such as illustrated in which the load would attempt to pull piston 48 to the left creating a pressure in chamber 52, piston 112 will prevent any movement of piston 48 since the flow of fluid is blocked by piston 112. Piston 112 thus serves as a load check valve in the neutral position of the manual 12.

Piston 1 12 also permits free flow of fluid to chamber 52 when control valve 12 is actuated to position 44, to move piston 48 to the right as viewed on FIG. 1, since conduits 66 and 92 always contain the highest work port pressure in the system and the differential area of shoulder 126 plus the frontal surface area of nose 118 when pressurized act against bias spring 164 to move piston 112 to the right as viewed in FIG. 1.

Due to the advantage of having a primary and secondary logic means, such that a connection can be made as illustrated between conduit 92 and conduit 66 which will reflect the highest work port pressure of manual valve 12 without any influence of other manual valves and fluid motor stations in the system, an anticavitation valve can be of a simple construction using shoulder 126, to provide the free flow function, since shoulder 126 is always connected to the highest work port pressure of its particular manual valve 12. The anti-cavitation valve 10 is of relatively simple construction as compared to prior art valves, but yet due to its use in combination with the primary and secondary logic system can perform the function of both an anti-cavitation flow control valve and a load check valve.

It should be noted that although the anti-cavitation valve is illustrated in a separate valve body 110, such a valve can be in a common body with the manual valve 12.

Various features of the invention have been particularly shown and described, however, it should be obvious to one skilled in the art that modifications may be made therein without departing from the scope of the invention.

What is claimed is:

1. A fluid system including an anti-cavitation valve, a reversible fluid motor and a manual control valve having an inlet means and arranged to control said motor, said manual control valve having a pair of work ports connected by fluid lines to said reversible fluid motor, said anti-cavitation valve being interposed in one of said lines and comprising a housing having a bore extending therethrough, a piston in said bore having a fluid responsive area thereon, differential pressure responsive automatically selective valve means connected to the work ports of said manual control valve to select the highest pressure in either of said work ports, conduit means connecting said fluid responsive area to said selective means to transmit said selected highest pressure, means biasing said piston to its closed position to prevent flow of fluid through said one line, said biasing means and said highest pressure positioning said piston whereby flow of fluid from said motor through said one line will be controlled to prevent cavitation in said fluid motor.

2. A fluid system as claimed in claim 1 including damping means to cushion closing movement of said piston.

3. A fluid system as claimed in claim 1 wherein said anti-cavitation valve piston has a nose portion and said anti-cavitation valve further includes a seat portion, said biasing means urging said piston nose portion against said seat portion to interrupt fluid communication in said one line.

4. A fluid system as claimed in claim 3 wherein said seat member has a damping means associated therewith to cushion movement of said piston into engagement with said seat.

5. A fluid system as claimed in claim 4 wherein said damping means comprises a metering slot formed in said seat member to provide partial communication of fluid through said one line as said piston approaches its position in engagement with said seat member.

6. A fluid system as claimed in claim 1 wherein said fluid responsive area of said piston comprises a shoulder.

7. A fluid system as claimed in claim 1 wherein said manual valve includes a pair of control ports connected to said shuttle valve means, each of said control ports being connected to one of said work ports in the operative positions of said manual valve whereby said control ports each are connected to one of the fluid lines to the fluid motor in each operative position of said manual control valve. 

1. A fluid system including an anti-cavitation valve, a reversible fluid motor and a manual control valve having an inlet means and arranged to control said motor, said manual control valve having a pair of work ports connected by fluid lines to said reversible fluid motor, said anti-cavitation valve being interposed in one of said lines and comprising a housing having a bore extending therethrough, a piston in said bore having a fluid responsive area thereon, differential pressure responsive automatically selective valve means connected to the work ports of said manual control valve to select the highest pressure in either of said work ports, conduit means connecting said fluid responsive area to said selective means to transmit said selected highest pressure, means biasing said piston to its closed position to prevent flow of fluid through said one line, said biasing means and said highest pressure positioning said piston whereby flow of fluid from said motor through said one line will be controlled to prevent cavitation in said fluid motor.
 2. A fluid system as claimed in claim 1 including damping means to cushion closing movement of said piston.
 3. A fluid system as claimed in claim 1 wherein said anti-cavitation valve piston has a nose portion and said anti-cavitation valve further includes a seat portion, said biasing means urging said piston nose portion against said seat portion to interrupt fluid communication in said one line.
 4. A fluid system as claimed in claim 3 wherein said seat member has a damping means associated therewith to cushion movement of said piston into engagement with said seat.
 5. A fluid system as claimed in claim 4 wherein said damping means comprises a metering slot formed in said seat member to provide partial communication of fluid through said one line as said piston approaches its position in engagement with said seat member.
 6. A fluid system as claimed in claim 1 wherein said fluid responsive area of said piston comprises a shoulder.
 7. A fluid system as claimed in claim 1 wherein said manual valve includes a pair of control ports connected to said shuttle valve means, each of said control ports being connected to one of said work ports in the operative positions of said manual valve whereby said control ports each are connected to one of the fluid lines to the fluid motor in each operative position of said manual control valve. 